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I know, yet another brake thread. But this is different and I can't find anything like it on thread histories.
The car
'71 roadster. PB. 350 auto.
It's owned by a very good friend. He inherited it a year ago from his father-in-law when he passed.
The brakes were a miss-mash of replaced parts, etc. They worked great but he had an issue with them 'sticking' after they got hot. Then a caliper leaked. Since the parts were a mix, he wanted to go through everything since his wife will drive it a lot.
I worked with him and we replaced: MC, all calipers (Lonestar), all hoses, new pads, etc.
Bench bled the MC and power bled everything 2X.
The problem
We tested for leaks and found none. So he took it for a few short drives. Great pedal. No leaks. No lock ups unless he really mashes the pedal and then it's controlled.
No problem on short drives. He takes it for a longer drive and noticed, after it's been driven for a bit, that he 'felt like he was loosing HP', the 'brakes still worked great', but 'something wasn't right'. He pulled over and the rear brakes 'were smoking'. He let things cool and it home drove fine, no problem - but he also made sure to not use the brakes any more than he had to. So he took if for another long drive: same thing happened. Let it cool, all is well.
He checked the MC - fluid still right where it should be. Checked for leaks - nothing.
Our theories
I'm thinking one of two things.
Parking brake issue? Not sure why it would only show up after longer drives though?
Proportioning valve?
Please chime in with your thoughts. Really appreciate your help. I'd like to help him get it going since we're finally into good weather and I'd like them to enjoy!
I thought I'd close the loop on this one with what we found in case it can help someone in the future. And a big thank you, as 67:72, theandies, HeadsU.P, and others were spot on with ideas.
This was a '71 that my friend inherited from his FIL, so he didn't know the repair history. It's a nice car but we've had to do some work (carb, tuning, and more) and it's now road worthy. I've had fun helping them as he and his wife are super nice and his MIL was in tears when she met me because she was so thankful that I was helping them get her late husband's vette back on the road in the family. Here's what we found on the brakes - there were 2 issues...
The parking brake mechanism turned out to be very rusty/crusty. When he used the parking brake and released it, the mechanism (and partly the cable) did not release completely and that's why the rears ended up 'smoking' after driving a bit. So (he did most of the work) the parking brakes were completely redone, cable and all. We thought for sure that was it. It was only part of the problem.
The master cylinder was not original and he wanted it replaced with all the calipers, etc. Unfortunately the core was tossed before any visual checks could be made. When he took the car out for a ride after the parking brakes were fixed, he had a similar issue - after a while the brakes would just 'bind'. There was really only one item left to check - refer to post #2 and a few others. You guessed it. The booster push rod was too long for the new master as shown in the photo below. It turned out that whoever replaced the master installed an adjustable rod so it was easy to fix.
His brakes are now working perfectly. Many thanks to you all for your help! Best, Paul
No expert, but here goes:
Since all is new, it's not the usual internally swelled rubber hose suspects...
On another forum someone was having similar heat issues. For a C3's system, the advice was two-step and both had to do with the master cylinder. #1: the booster push-rod may be applying slight pressure to the brake pads, heating up the system, and causing the fluid to expand back into the master; #2: if the master is full up, there's no room for the expansion against the sealed cap which then applies more pressure on the brake pads.
First order of business is to make sure the push-rod is set properly - no need to rebleed the system as the M/C will pull forward from the booster without opening any of the system to atmosphere. After that leave the master with a 1/2" air space to the cap.
Last edited by barkingrats; Apr 21, 2024 at 11:30 AM.
All 4 brakes were smoking or just the rear? If just the rear then I would check the parking brake (which is actually a small drum brake in the rear rotors).
Normally I would say 67:72 is spot on about the booster rod gap clearance.
The brake pedal is somewhat heavy. If it was not attached to anything it would slam or sink to the floor by itself.
That gravity pressure from the pedal has to have some leeway or the hydraulics are under pressure constantly.
The pads need to have some room for the caliper pistons to retract. This is where the "gap" or "play" comes in between booster rod and MC piston.
That is about a 1/16 of an inch. 0.060
Basically, if the gap is too wide there is a delay between depressing the pedal and actually activating the MC. It may only be an inch but feels like a foot of travel.
Too small a gap, and the pads / pistons are under pressure, meaning a constant drag against the rotor.
All of the above will usually be noticed on all four calipers, not just the fronts or rears.
Check the parking brake cables. Is the exhaust laying on any portions of it, applying tightness?
#1 for either parking brake system or booster pushrod.
Depends if 2 or 4 wheels get hot.
You could jack the car up, all 4 wheels, and hand rotate the tires while someone slightly applies the brakes.
You need some pedal free-play before the brakes start working.
Then do the same with the park brake handle.
You'll find it.
I found a lot of weird brake problems that way
Last edited by leigh1322; Apr 21, 2024 at 09:02 PM.
I thought I'd give an update. I was gone all day, but my friend pulled the rear rotors off and...
The drivers side rotor had to be 'wiggled back and forth' to get it off - like the parking brake was too tight. Normal or not?
The passenger side had a broken top spring as shown below. There is a youtube video that shows an owner rebuilding his parking brakes that had been 'smoking' and the cause was a broken spring just like this. So we're hopeful.
I'm going over tomorrow to looks things over. I think I have a parking brake rebuild kit; if not he'll order one.
Really appreciate all the insights. Hopefully this will do it, but still very open to other ideas to check while we're in there. Thanks! Paul
Test them yourself while it's up in the air. 2 man job.
rotate by hand.... push pedal 1" ...repeat....
Then you will know if they are good or not...no guessing.
I'm thinking if your looking at YouTube video's, I can't help you.
Kind of funny. I've found 'some' youtube vids to be very helpful, while others are a complete waste of time. I almost always know enough to know the difference. As you know there are a lot of 'quirks' in C3s and it's great to learn from others experience (and mistakes). There are very helpful members of the forum that regularly share experience with pics and a few have created videos too. A handful of vendors do the same, very helpful. One of the best series of helpful write-ups and vids was Ernie (RIP) at Wilcox. IMO he was the most helpful vendor I've seen in my C3 years.
I thought I'd close the loop on this one with what we found in case it can help someone in the future. And a big thank you, as 67:72, theandies, HeadsU.P, and others were spot on with ideas.
This was a '71 that my friend inherited from his FIL, so he didn't know the repair history. It's a nice car but we've had to do some work (carb, tuning, and more) and it's now road worthy. I've had fun helping them as he and his wife are super nice and his MIL was in tears when she met me because she was so thankful that I was helping them get her late husband's vette back on the road in the family. Here's what we found on the brakes - there were 2 issues...
The parking brake mechanism turned out to be very rusty/crusty. When he used the parking brake and released it, the mechanism (and partly the cable) did not release completely and that's why the rears ended up 'smoking' after driving a bit. So (he did most of the work) the parking brakes were completely redone, cable and all. We thought for sure that was it. It was only part of the problem.
The master cylinder was not original and he wanted it replaced with all the calipers, etc. Unfortunately the core was tossed before any visual checks could be made. When he took the car out for a ride after the parking brakes were fixed, he had a similar issue - after a while the brakes would just 'bind'. There was really only one item left to check - refer to post #2 and a few others. You guessed it. The booster push rod was too long for the new master as shown in the photo below. It turned out that whoever replaced the master installed an adjustable rod so it was easy to fix.
His brakes are now working perfectly. Many thanks to you all for your help! Best, Paul
Good job. Don't let anybody discourage you from learning.
Originally Posted by Hopper12
Kind of funny. I've found 'some' youtube vids to be very helpful, while others are a complete waste of time. I almost always know enough to know the difference. As you know there are a lot of 'quirks' in C3s and it's great to learn from others experience (and mistakes). There are very helpful members of the forum that regularly share experience with pics and a few have created videos too. A handful of vendors do the same, very helpful. One of the best series of helpful write-ups and vids was Ernie (RIP) at Wilcox. IMO he was the most helpful vendor I've seen in my C3 years.
I'm thinking if your looking at YouTube video's, I can't help you.
Boy you really have something against people that find youtube videos useful huh? What exactly makes them inferior than someones opinion of a forum? Yes a person should watch multiple videos on a subject and use common sense but they can be a great resource. It was for me anyway.
Thanks for the follow-up Paul. Great you guys got it figured out. And, awesome that you stepped up to help out the family with there memories of Dad and his C3.
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Brake experts: please provide insights
